3D: How does it work?

posted by Victor H. / Mar 03, 2011, 6:09 AM

The third dimension has been explored by 3D enthusiasts way back in the early 20th century when the first stereoscopic films appeared, but it wasn't until recently that 3D took the spotlight with an array of TV sets, portable game consoles and most recently phones. The 3D hype is still in its early days, but more and more people are considering the option. But honestly – always watching TV with the glasses? If you are not 15, chances are you tried watching a 3D movie at home for half an hour, shrugged your shoulders and took off the damn glasses to never try it again. There should be a better way! And mobile technology has it, but just how does it work?

Currently, there are
only a few gadgets featuring glasses-free (also called
autostereoscopic) 3D displays. The LG Optimus 3D and the
Nintendo 3DS are probably the most popular ones and both use a
special screen technology called parallax barrier. The 3DS even
allows for gradual control of just how much of a 3D effect you want.
In addition, both of them (and a slew of recently announced
camcorders) support recording in 3D via a dual-camera setup.

Our brain processes what we see to achieve the feeling of depth

Why do we see in 3D?

To understand the whole mechanism we
have to go back to the basics of human vision. We see the
world in 3D mostly because of our vision, which is similar to that 3D
camera setup. Our left eye sees one thing and our right eye sees a
slightly different picture. The eyes are spaced apart and each one of
them takes a different stream of information from its own viewpoint.
The brain mashes it all up in one beautifully deep 3D picture. That,
of course, is aided by cues about depth from the shades and motion of
objects. Similarly, the two camera sensors are placed at an inch or
so of a distance and both simultaneously capture content, just like
your eyes. The left camera records information for the left eye,
while the right camera records its stream for the right eye. That's
exactly how the dual camera setup on the upcoming LG Optimus 3D and
T-Mobile G-Slate works. From here on, the brain does its thing and
voila - you have 3D! But how do we then give each of the eye the
respective video?

Stereoscopic imaging - gotta wear shades!

That's the magic of 3D. In the stone age of the 20th century it was simple – just get a pair of red/blue (cyan to be exact) glasses that say “geek” better than if you had it tattooed on your forehead. Those are called anaglyph and have the advantage of being the cheapest ones you can easily make from cellophane at home. The trickery relies on the two video streams edited to show one in red and the other in cyan. The glasses then act as filters – the red lens allows the “reds” stream and blocks the cyan one, while the cyan feeds only the cyans to the respective eye. The rest as you might have already guessed is brain work.

Anaglyph vs polarized glasses

But then in the movie theaters, you watch something completely different. While we still have two streams of video, this time they are superimposed onto the screen using different filters. What you wear is polarized glasses, the reason is that they have differently polarized lenses. Usually, we have a vertical polarization on the one, allowing only the vertically polarized content to pass through, and a horizontal polarization on the other lens, which in turn gives you the horizontally polarized stream. Hence, each of the eyes sees a different picture and we're back to the brain doing the rest. In this case, though, you have a much better quality since no color information is lost as is the case with anaglyph (red/cyan) glasses. While polarized glasses themselves are
relatively cheap, your TV will need a screen with polarized coating
allowing each eye to see every other line, which comes at a higher
cost. The first TVs with the technology have already hit the market,
but the price tag is pretty steep – prepare nearly $3500 for the
first 65-inch Vizio Razor LED passive 3D TV.

- Anaglyph glasses pros and consPros: Cheap, can be made at home, don't require special equipmentCons: Some of the colors are lost, the effect is not that submersive

And finally, some of you have (or most
probably will have) 3D TVs at home, which require the fancy and
rather expensive shutter glasses. The previous two types of
glasses are known as passive since they don't need a power source
(and that much of an investment as the shutter glasses!), but the
shutter glasses come with a battery. The shutter lenses are actually
small LCD screens that alternate the picture for each of the eye at
rapid speed. To achieve this they simply dim and turn back on in
the blink of an eye. At the same time, your 3D TV first shows the
stream for the left eye while the right lens dims the picture for the
right eye, then the stream for the right eye appears, while the left
lens is dimmed. This alternation happens at a rate of about 120 times
per second. The shutter glasses on their
part are usually synchronized with the TV via infrared or RF. This
allows each of the eyes to get the corresponding picture and pass it
to the brain for achieving the effect of depth. You might wonder what
happens to the frame rate and rightfully so. The consecutive
switching between two streams cuts it in half and this is why you
might sometimes see jittery video on your 3D TV.

But with all this said, how does the filtering of the two recorded video streams happen without the glasses?

The parallax barrier allows each eye to see a different image

Here's when you need something way out of the ordinary. The LG Optimus 3D (and the Nintendo 3DS for that matter) uses the parallax barrier technology. Parallax might sound scary, but simply put it is the effect of seeing closer objects bigger and more distant ones – smaller. What matters most is the barrier however. It is just what you would imagine – a vertical slit plate on top of the traditional screen that blocks part of the image for each eye. The technology is somewhat limited to smaller screens, but yields good results without the geekines of wearing glasses. Check out our first hands-on encounter with the LG Optimus 3D to learn more about it and get your glasses ready for some 3D samples shot with the Optimus 3D here. Looks pretty neat doesn't it?

Finally, we can certainly think of a couple of ways to use 3D, but the sky is the limit in the future. And IBM's researchers are hypothesizing about holographic video calls by 2015, so we can see the future coming even faster than we ever expected. At least - with so many options - we can't complain about not having the choice, right?

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